This invention relates to a sample cup for use in holding specimens for spectrochemical analysis and more particularly to such a cup including means for venting the same.
Sample cups for spectrochemical analysis are used in the prior art to hold or contains liquid, solids and powdered specimens under normal atmospheric pressures, gas pressures or in vacuum for analysis such as energy and wavelength dispersive techniques and optical emission methods. Such cups, as indicated, are in widespread use.
Essentially the sample cup consists of three components as a cup shaped cell having a closed bottom and an opened top, an annular collar and a snap on ring. A typical prior art cup is shown in U.S. Design Pat. No. 238,693 entitled CELL FOR X-RAY SPECTROSCOPY OR SIMILAR ARTICLE issued on Feb. 3, 1976 to Monte J. Solazzi.
The collar and the snap on ring serve to secure a sheet of plastic material such as mylar to cover the open top of the cell when the hollow of the cell is filled with a specimen as the liquid, solid or powdered material to be analyzed. Such cells are available from many sources such as Chemplex Industries, Inc., of 140 Marbledale Road, Eastchester, N.Y. 10707.
The cells of the prior art have a recessed or depressed small area on the closed bottom surface of the cell which can be punctured or pierced by means of a sharp point such as the tip of a ball-point pen or some other device. The pierced hole serves as a vent as will be explained and is used to equalize pressure within the sample cup.
For spectrochemical analytical investigation of specimens or analytes characterized with high abrogation properties in air, the entire assembled sample cup with the plastic sheet covering the top may be emplaced within a vacuum or an inert gas environment. Under conditions where pressure equalization is not implemented, the plastic sheet will distend or bow outwardly due to the vacuum or lower pressure. This then places the surface of the sheet closer to the excitation source which may be an X-ray tube or other device. The surface of the sheet of plastic is commonly defined as the sample plane. A variation in the distance from the sample plane to the source of excitation operates to alter the intensity of the characteristic radiation of the analyte and also the intensity of radiation impinging upon the sample from the excitation source. The variations result in erroneous quantitative data and hence cannot be tolerated. As indicated for applications in a vacuum environment the thin plastic film distends or bows out (convex) which decreases the distance from the sample to the excitation source. For applications in a gaseous environment (positive pressure) the thin plastic film tends to be drawn into the hollow of the cell or provides a concave surface. This effect increases the distance between the sample plane and the excitation source resulting in lower values of analytical data.
In order to equalize the pressure the prior art had a section in the closed bottom surface of the cell which allowed one to pierce a hole in the cup or vent the cup. In any event the technique relied on the skill of the operator and if too much force were employed the hole would be too large, the sample might become contaminated or the parts of the cup dislodged.
Thus the prior art technique is not a convenient way of providing venting of sample cups.
It is therefore an object of the present invention to provide an improved sample cup including venting means which enable an operator to provide venting in a rapid and precise manner.